Production of pure aromatic hydrocarbons



Jan. 17, 1967' H.WIRTH ET AL 3,299,158

PRODUCTION OF PURE AROMATIC HYDROCARBONS Filed Sept. 8, 1964 4Sheets-Sheet l Irrremors HA NS WIRTH KARL -HEINZ E/SENLOHR Jan. 17, 1967,'w ET AL 3,299,158

PRODUCTION OF PURE AROMATIC HYDROCARBONS Filed Sept. 8, 1964 4Sheets-Sheet 2 l'm e/vzors HA N 8 WI I? TH KA RL. HE/NZ E/SENLOHI? giaamw a Jan. 17, 1967 H.W|RTH ETAL PRODUCTION OF PURE AROMATIC HYDROCARBONS4 Sheets-Sheet 5 Filed Sept. 8, 1964 & Ex 5 Q Qm QM l'm emans" HANSWIRTH KARL HE/NZ EISENLOHQ United States Patent Office 3,299,1l58Patented Jan. 17, 1967 3,299,158 PRODUCTION OF PURE AROMATICHYDROCARBONS Hans Wirtlr and Karl-Heinz Eisenlohr, Frankfurt am Main,Germany, assignors to Metallgeselischaft Aktiengesellschaft, Frankfurtam Main, Germany Filed Sept. 8, 1964, Ser. No. 396,801 Claims priority,application Germany, .lune 4, 1960, M 45,554 2 Claims. (Cl. 260-674)This application is a continuation-in-part of copending applicationSerial No. 115,001, filed June 5, 1961, now abandoned.

The present invention relates to a process of producing pure aromatichydrocarbons from mixtures containing aromatic and paraffinichydrocarbons employing a selective solvent, a mixture ofN-methyl-pyrrolidone and more than water.

More specifically this invention is directed to obtaining pure aromatichydrocarbons from hydrocarbon mixtures, especially coke oven benzene,low temperature carbonization benzene, reformates from petroleumprodnets, and cracked benzine resulting from cracking of petroleumfractions, by extraction with a selective solvent consisting ofN-methyl-pyrrolidone with more than 10% and as much as up to 40% water,specifically 35% water. The starting hydrocarbon mixture may be purifiedin a preliminary step, for example, by catalytic hydrorefining in whichpolyunsaturated hydrocarbons are selectively hydrogenated and may betreated with bleaching earth or other known agents.

Pure aromatics as employed herein means aromatic hydrocarbons which areusable as starting materials directly in chemical synthesis andconversions which are sensitive to impurities and also means those whichcomply with the customary purity requirements for these raw materials.The purity requirements for aromatics differ somewhat from country tocountry and according to the purpose for which the aromatics are to beused. However, certain minimum requirements or standards exist. For puretoluene, a refractive index of at least n =1.496 and generally at least1.4966 is required in comparison with that of chemically pure toluene of1.49693. Pure C aromatics are frequently not used in the form of singleindividual components, that is the ortho, meta, and para xylene andethylbenzene are not separated individually, but rather employed as purexylene or a C cut. The usual specifications or purity requirements forthis pure xylene or C cut originated at a time when the xylene wasrecovered from coal tar and therefore was by nature free fromnon-aromatics. Accordingly, the provision of a boiling range of, forexample, 135145 C. was suflicient to obtain the then desired purity.While pure xylene which satisfied these purity requirements could beproduced from a starting mixture containing non-aromatics, the startingmixture containing non-aromatics was not suflicient for work up to theindividual components, as, for example, ortho xylene for the productionof phthalic anhydride, para xylene for the production of terephthalicacid and ethyl benzene for the production of styrene, since thenon-aromatic content could not be reduced to about 0.05 to 0.1%.

Numerous processes have been known for a long time for separatinghydrocarbon mixtures into a rafiinate phase relatively enriched with oneor several groups of materials and an extract phase relatively enrichedwith other groups of materials with the aid of a selective solvent. Inmany cases, also heterocyclic ring compounds have been used in theseseparation processes as the selective solvent.

Thus, for example, olefines have been separated from diolefines withgood efficiency employing N-methyl pyrrolidone containing 1-15% water,preferably 37% water, as the selective solvent. Lactones, particularlybutyrolactone, have been suggested for separating aromatics fromhydrocarbon mixtures. It is known, for example, to obtain a relativelyhigh concentration of toluene from a toluene-heptane mixture employingbutyrolactone having a water content of 25 or to recover a concentratedextract containing up to about 98% aromatics from a light hydroformateby means of butyrolactone having a water content of 10%. Also thenoncontinuous separation of an extract concentrated in aro matics havinga refractive index of n =1.5691 from a recycle oil having a 25%aromatics content is known by extraction with N-methyl-pyrrolidonecontaining up to 5% water, just as the production of extracts havingrelatively high aromatic content, up to 98%, is known with the aid ofcompounds of the oxazolidone series having a water content of 120%.

While these processes in general have as a purpose the enrichment orconcentration of aromatics by selective extraction, they do not concerna partial step of a process for the production of the purest aromaticsbut only of relative enrichment. These processes are completely separatefrom those which are required for the production of pure aromatics. Evenan enrichment or concentration to an aromatic content of 98%corresponding to an impurity content of 2%, that is a content ofnon-aromatic impurities, is not satisfactory for the purposes of thisinvention since this impurity content is around 20-200 times higher thanpermissible for work up to pure hydrocarbons.

It is known that the separation effect of a selective extraction with agiven ratio of distribution of aromatics to non-aromatics in a specificsolvent can be improved by increase of the number of stages to certaindegree the basis of economy to use both means as little as possible.

Likewise it is known that the selectivity of many solvents can beincreased by dilution with water, but only at the cost of absorbingcapacity, charging capacity or absolute solvent power given, that is theamount of extract which a given amount of solvent can absorb. Thedisadvantage can be balanced somewhat by an increase in temperature, butan increase in temperature itself provides a series of otherdisadvantages, such as the necessity of making the apparatus pressureresistant.

These known means have therefore been used only in a few cases in orderto achieve the high requirements of purity which are placed on anextract suited for processing to pure aromatics.

In order to achieve the given specifications for the final product,olefines and naphthenes must be kept out of the extract more completelythan is possible with most of the usual solvents. Thus the cyclohexanecontent of benzene, for example, may be no higher than 0.2% if thebenzene is not to have a melting point below 5.4 C. If the benzene musthave a melting point of 55 C, then the cyclohexane content may not evenexceed 0.01%. The ratio with the corresponding impurities in toluene andXylenes is different, but is effected in the same manner.

The solvent employed for extraction must therefore be extremelyselective with regard to the separation of benzene and cyclohexane inorder to obtain an extract substantially completely free of cyclohexanesince subsequent separation of benzene through rectification isextremely expensive due to the very close vapor pressures of these twocomponents. Thus, for example, to lower the cyclohexane content of animpure benzene from 1% to 0.01% a column having 60 theoretical platesand a reflux of 150 times is necessary calculated on removal of thedesired compounds as an azeotrope which must be removed in an amount ofabout 2.5%. The recovery of an extract which is only enriched inaromatics from a mixture of aromatics and non-aromatic hydrocarbons bysolvent extraction is basically different from recovery of an extractuseful for processing to pure aromatics in that in this instance theextract must be practically free of all non-aromatics, that is, also ofsuch compounds whose solubility in most solvents which are used normallyfor solvent extraction is very similar to the solubility of singly or atleast normally separated aliphatics.

It is of especial significance in this connection that the viscosity ofthe solvent be as low as possible. If the viscosity is too high then theexchange of materials occurring in the extraction column, as, forexample, in a column filled with screen bodies, a column having rotatingdisk contactors, a spray column or the like, is considerably reduced. Inorder to force this a battery of special mixer-separators is necessary.In such a case separation of the two phases into individual compoundspresents practically insurmountable difficulties. Therefore the use of asolvent having a viscosity which is too high must be offset by anincrease in temperature which brings with it other difiiculties such asthe lowering of selectivity, increasing of decomposition and corrosionprocesses and the necessity of using pressure resistant apparatus.

Only a few of the numerous known selective solvents can be used forrecovery of pure aromatics from mixtures containing non-aromatics, whileall other solvents are unusable on various grounds of technical andeconomic difficulties. Thus, for example, alkane dinitriles,y-butyrolactone and cyanoether of diethylene glycol are unsuitable dueto lack of chemical and thermal stability.

Many of the suggested compounds or compositions such as, for example,dimethyl hydantoin also precipitate and are therefore not evenconsidered technically. Several others, as, for example, furfurol,phenol and cresol have very little selectivity which cannot be broughtup to the required degree by addition of water.

The one group of solvents which was used with some success heretoforefor recovery of an extract suited for further processing to purearomatics from aromatic rich hydrocarbon mixtures is the lowerpolyethylene glycols, especially di-, triand tetraethylene glycol. Thesehave suitable selectivity for aromatics and against olefines andnaphthenes in order to achieve an adequately pure extract in the usualnumber of stages.

However, their absolute solvent power is small and their viscosity highso that it is necessary to adapt the extraction apparatus to essentiallyhigher temperatures, especially about 130 C., in order to bring thecharge and viscosity within a range in which the solvent ratio isoperable to some degree and the dimensions of the extractor aretechnically suitable. Moreover, with this solvent it is necessary tohave a solvent ratio of about 20 parts by weight of solvent for eachpart by weight of aromatic solvent in the starting mixture.

It is accordingly an object of this invention to provide a selectivesolvent composition and a selective extraction process which is veryselective in removal of aromatics from hydrocarbon mixtures containingboth aromatics and non-aromatics and which does not have thedisadvantages set out above.

It was found according to the invention that the selectivity ofN-methyl-pyrrolidone, herein referred to as NMP, heretofore suggested asa selective solvent, and its ability to separate impurities fromhydrocarbon mixtures, such as olefines and naphthenes, can be increasedby diluting it with a precise determined amount of water. The resultingmixture of NMP and water has a selectivity which is at least equivalentto an if desired exceeds that of polyethylene glycols. However, theviscosity is lower and the absolute chargeability, that is the amount ofaromatics able to be dissolved in the solvent mixture of the invention,is higher than that of polyethylene glycols. For example, according tothe invention a mixture of NMP and 15% water at 20 C. has a viscosity of4.2 cs. contrasted to 43.5 cs. for tetraethylene glycol at the sametemperature. Therefore with a mixture of NMP and 15% water as theextraction agent, for example, 2.5% cyclohexane can be separated from amixture containing 25% benzene, 25% toluene, 10% xylene and 40%non-aromatics, that is a cyclohexane content corresponding to 10% of thebenzene content, using an extraction apparatus having 22 theoreticalplates.

A pure benzene, that is one having a melting point of at least 5.5 C.corresponding to a purity of at least 99.99% can be obtained from theresulting mixture directly by a simple distillation. This high purityaccording to the invention is however not obtained by increasing costsor significant reduction of yield because benzene having the abovepurity can be obtained in yields of 99.5% based on the benzene contentof the starting mixture. Since NMP is not corrosive and is thermally andchemically stable and can be produced on a large scale at a practicalprice, all the disadvantages of extraction solvents employed heretoforeare overcome by the solvent mixture of the invention. Also theessentially higher boiling point of 204 C. as compared to that of thepure aromatics to be recovered not only permits the aromatic extract tobe recovered overhead by distillation of the extract phase and thesolvent to be recovered as the pot product, which provides advantages inheat efficiency, but also permits the composition to be carried out withfewer plates (about 5 to 10 plates according to the composition of theextract) and lower reflux ratio.

The limits of dilution of the NMP according to the invention lie betweena water content of over 10% and up to a maximum of 40%. NMP having awater content up to about 10% has the disadvantages of all other knownextraction solvents in that, with increased charge in aromatics from amixture containing non-aromatics the nonaromatics are taken up equallyas well as the non-aromatics whereby the charge may be increased innon-aromatics even more strongly in aromatics. However, it was foundthat just the opopsite of this well known phenomena occurs if NMP with awater content of more than 10% is used as a solvent. The change in theseparation into the counterparts occurs initially above a water contentof 10%, that is, after exceeding a critical aromatic content of theextract phase decreasing amounts of nonaromatics are absorbed, if thecharge of the extract phase with aromatics is increased. The limits ofthe water content of the solvent and the aromatic content of theextract, where this sudden reversal in absorbing properties occurs,depends on several factors, such as the exact composition of thearomatic and non-aromatic constituents in the starting mixture and aboveall the operating temperature. By exceeding the lower limits of thewater content, i.e., above 10% water, in each case there is assurancethat the separation will occur for practically every combination in thestarting mixture at temperatures corresponding temporarily to at leastthe surrounding temperatures and therefore can be maintained withoutartificial cooling.

The selectivity for aromatics over non-aromatics and also overcycloparaffins and olefins increases further by increasing the additionof water while the capacity of the selective mixture according to theinvention decreases only slightly. The first strong decrease in capacityor chargeability occurs when the water content exceeds 40%. On thisbasis the critical limits of the water content of selective solventaccording to the invention are above and up to 40%, specifically aboutto 35%.

The increase in selectivity achieved in this manner while maintainingsolvent capacity is mostly suflicient alone in order to recover anextract directly from a starting mixture available from an industrialprocess with a technically efiicient number of steps which extractsatisfies the high purity requirements in order to use it for furtherprocessing to pure aromatics. Nevertheless, this selectivity issufiicient to permit recovery of an extract having the required purityin a single step by using the extract recycle and/ or the countercurrentflow of an anti-solvent, both known per se and in other combinations.According to the invention low boiling hydrocarbons are used as ananti-solvent, that is, hydrocarbons which boil below the boiling rangeof the aromatic fraction to be recovered, preferably pentane.

Usable starting mixtures are all hydrocarbons stemming from thepurification of solid and volatile combustible materials, especiallycoke oven benzene and low temperature carbonization benzine, as well asreformates of petroleum products and cracked benzines resulting fromcracking of petroleum fractions to produce olefines. The startingmaterial can also be purified in known ways, for example, by catalytichydrorefining and treated with bleaching earth or other known agents.

The process of the invention is hereinafter described by way ofillustration with reference to the accompanying drawings wherein:

FIGURE 1 is a schematic diagram of an apparatus suitable for separatingaromatic hydrocarbons from a hydrocarbon mixture containing aromatic andnon-aromatics;

FIGURE 2 is a schematic diagram of an apparatus suitable for separatingaromatic hydrocarbons according to the invention wherein an 'antisolventis employed to increase the selectivity of the solvent mixture;

FIGURE 3 is a three component diagram for a mixture of benzene, hexaneand N-methyl pyrrolidone containing 25% water at C. showing the resultsof tests for equilibrium; and

FIGURE 4 is a graph showing a comparison of known solvents with solventmixtures according to the invention.

The process of the invention comprises feeding the starting hydrocarbonmixture into a multistage extractor, for example, into about the middleof an extraction column, feeding NMP containing more than 10% and up toabout 40% water as the selective solvent into one end of the extractorand part of the resulting extract into the other end of the extractor.The rafiinate phase, freed extensively of aromatics, is removed from theextractor at the end into which the selective solvent is fed and theextract phase, practically free of non-aromatics, from the nd into whichthe extract recycle or the anti-solvent is It is especially advantageousif an anti-solvent is passed through the extractor countercurrent to thefiow of the selective solvent at the same time and an extract recycle isemployed since thereby the charge of the solvent with aromatics isshifted in the area in which the absorption capability for non-aromaticssurprisingly declines again. The simultaneous use of an anti-solvent andan extract recycle makes is possible to employ both supplementalmaterials together in smaller amounts than was necessary With eachalone. This special feature of the invention permits use of anessentially lower solvent ratio in comparison to other processes andalso processing to the highest purity of aromatics under that with otherprocesses. Thus, for example, the purest benzene having a melting pointof 5.5 C. is recovered according to the invention using a solvent ratioof only 5-7 parts by weight solvent for each part by weight of aromaticscontained in the starting mixture. This preferred embodiment of theinvention is effected simply by introducing the extract recycle alongwith the anti-solvent into the extractor at the end from which theextract phase is removed. In this case it is advantageous to strip theextract phase by dis tillation such that the extract results which ispractically free of anti-solvent but an anti-solvent is produced stillcontaining essential amounts of extract.

The favorable aspects of the balance of constituents is demonstrated inthe following Table 1 which gives the results of two tests usingmixtures of benzene and hexane. Test 1 was carried out using a mixtureof by volume benzene and 30% by volume n-hexane while Test 2 was carriedout employing a prepared mixture of 92% by volume benzene and 8% byvolume n-hexane. NMP containing 25% by volume water served as theselective solvent and was introduced in an amount of 1 part by volumeselective solvent, i.e., NMP containing 25 water, to each part. Theconcentration data is based on the solvent free mixture.

TABLE 1 Mixture 10 parts by volume of N-methylpyrrolidone plus 3.3 partsby volume of water.

Solubility of pure benzene in this mixture at 20 C 6 parts by volume.

Test 1 Test 2 Composition of the refining phase:

Percent by volume of benzene 59 .8 87 .4 Percent by volume of hexane 40.2 12 .6 Composition of the extracting phases.

Percent by volume of benzene 95 .5 98 .4 Percent by volume of hexane 4.5 1 .6

The hydrocarbon mixture which was separated consisted of 50%non-aromatics having a boiling range of from 50 to 160 C., 23% benzene,15% toluene, 18% xylene and 4% higher aromatic substances. The solventmixture used in the separating process consisted of 78.5% ofN-rnethyl-pyrrolidone and 21.5% of water.

Referring to FIGURE 1, extraction column 1 has an efiiciency of 20theoretical stages. The hydrocarbon mixture to be separated wasintroduced through supply line 2 to a central stage of column 1. Thesolvent was introduced into column 1 at the upper end thereof throughthe solvent supply line 3 and was enriched with aromatic substances asit proceeded downwardly through the column. 300 parts of the solventwere added for each 100 parts of starting mixture.

The solvent which contained dissolved aromatics free from non-aromatichydrocarbons was discharged through line 4 at the lower end of column 1.The non-aromatic hydrocarbons were discharged from the top of column 1umn 8. In this column the aromatics were separated from the solvent by adirect flow of steam which entered the column through line 26. A mixtureof aromatics and water vapor was discharged from the stripper column at9. This mixture was then condensed in the cooler 10 and flowed into theseparator 11 within which it was separated into water and an aromaticphase. The resulting aromatic substances which were discharged from theseparator 11 through line 11A were taken off at the point 12 anddischarged through line 13. These aromatic substances resulting wereseparated by means of a simple distillation into the pure aromaticconstituents consisting of benzene, toluene and xylene.

A portion of the aromatic substances which were discharged fromseparator 11 were recirculated into column 1 through line 6.

Water was withdrawn from separator 11 through line 14 and a portion ofthis water was discharged through line 15.

The remaining portion of the water was passed through line 16 andintroduced into the regenerated solvent from lines 17 and 23.

The solvent which was free from aromatic substances was discharged fromcolumn 8 through line 17. The water content of this solvent was thenincreased to the necessary amount by water introduced through line 16and the solvent was then introduced into column 1 through line 3.

The non-aromatic substances which were discharged through line fromcolumn 1 contained a small quantity of solvent. This solvent wasseparated from the nonaromatic substances in column 18 by a flow ofsteam introduced through line 27. The non-aromatic substances wereintroduced into column 18 through line 19 and were discharged from thecolumn through line 20, which conveyed them to cooler 21 and separator22 wherein the substances were separated from water. The non-aromaticsubstances were then discharged through line 25. Small quantities ofwater were discharged from separator 22 through line 24. The solventfree from non-aromatic substances was discharged from column 18 throughline 23 and recirculated through column 1 together with the solventwithdrawn from column 8 through line 17.

In an extraction conducted according to the above process, pure benzenehaving a crystallization point of 5.5 C. was obtained, as well as hexaneand toluene, having a purity greater than 99.8%.

Example 2 The same starting mixture as employed in Example 1 wasprocessed in the apparatus as described in FIGURE 2 with a solventconsisting of 85% NMP and 17% water. The apparatus employed in theexample consisted of a ZO-stage extractor 31 into which the startingmixture Was introduced at one of the central stages through line 32. Thesolvent comprising NMP and water was introduced through line 33 in theratio of 360 parts of solvent per 100 parts of star-ting mixture. Thesolvent was discharged from the column through line 34 together witharomatic substances. A hydrocarbon mixture having a boiling point below50 C. and comprising primarily pentane was introduced as an anti-solventinto the extractor 31 through line 35. The pentane passed upwardlythrough column 31 countercurrent to the fiow of NMP and was dischargedfrom the column through line 36 together with non-aromatic substancescarried along therewith.

The NMP and aromatic substances withdrawn through line 34 wereintroduced into stripper column 38 through line 37. In this column adirect flow of steam was employed to separate the dissolved aromaticsubstances from the NMP. The solvent was then recirculated through lines39 and 33 into column 31.

The aromatic substances and water were discharged from column 38 throughline 40, subsequently condensed in cooler 41 and separated into anaqueous phase and a hydrocarbon phase in separator 42. The requiredamount of water was introduced into the solvent through line 43 and theremaining water was discharged through line 44. The aromatic substanceswere then discharged through line 45 into distillation column 46 in theupper part of which pure benzene was obtained at 47. The pure benzenewas discharged through line 48.

The solvent withdrawn from column 31 still contained small quantities ofpentane with which it was in contact in the column. The pentane wasdistilled in and removed from the top of column 46 through line 49 andrecirculated into column 31 through cooler 50 and line 51. The majorportion of the anti-solvent was discharged from the extractor column at36 together with some nonaromatic substances and was passed through line52 into distillation column 53. The small quantity of NMP which wascarried along with these non-aromatic substances was withdrawn fromcolumn 53 through line 54 and introduced into the recycled solventthrough line 33.

The pentane was distilled and removed from column 52 through line 55,condensed in cooler 56 and recirculated through lines 51 and 35.

Any non-aromatic substances remaining in column 53 were tapped therefromthrough outlet 57, condensed in cooler 58 and discharged through line59.

Stripping steam was introduced into the column 38 through line 60. Incolumn 53, however, the substances therein were heated by means of aheater coil 61 within which steam was circulated. The column 46 wassimilarly indirectly heated by a heater coil 62.

The residue resulting from column 46 consisted of toluene, xylene andhigher aromatic substances and was discharged therefrom at 63. Thisresidue can be introduced into another system of columns not shown inorder to obtain the individual constituents in their pure condition.

The process and system as described in this example produced a yield of99.5% benzene having a crystallization point of 5.5 C.

Our description in specific detail of the selected embodiments of theinvention will suggest various changes, substitutions and otherdepartures from our disclosure within the spirit and scope of theappended claims.

We claim:

1. A process for separating pure aromatic hydrocarbons boiling at aboutto C. from a starting hydrocarbon mixture consisting essentially ofaromatic and non-aromatic hydrocarbons comprising intimately contactingthe said hydrocarbon mixture with a selective solvent consistingessentially of N-methyl-pyrrolidone with more than 10% by weight and upto 40% by weight water whereby the aromatic hydrocarbons are dissolvedin the selective solvent to form an extract, and passing a mixtureconsisting essentially of a non-aromatic hydrocarbon anti-solventboiling below the aromatic hydrocarbons in combination with recycledextracted aromatics countercurrently through the resulting extract andrecovering the aromatic hydrocarbons dissolved in the extract in pureform.

2. A process as in claim 1 wherein pure benzene having a crystallizationpoint over 5.5 C. is recovered.

References Cited by the Examiner UNITED STATES PATENTS 2,799,627 7/1957Haensel 20896 2,840,620 6/ 1958 Gerhold et al 208-96 2,886,610 5/1959Georgian 260674 2,933,448 4/1960 Morin et al. 260-674 FOREIGN PATENTS812,114 4/1959 Great Britain.

DELBERT E. GANTZ, Primary Examiner.

C. E. SPRESSER, Assistant Examiner.

1. A PROCESS FOR SEPARATING PURE AROMATIC HYDROCARBONS BOILING AT AOBUT80 TO 160*C. FROM A STARTING HYDROCARBON MIXTURE CONSISTING ESSENTIALLYOF AROMATIC AND NON-AROMATIC HYDROCARBONS COMPRISING INITMATELYCONTACTING THE SAID HYDROCARBON MISTURE WITH A SELECTIVE SOLVENTCONSISTING ESSENTIALLY OF N-METHYL-PYRROLIDONE WITH MORE THAN 10% BYWEIGHT AND UP TO 40% BY WEIGHT WATER WHEREBY THE AROMATIC HYDROCARBONSARE DISSOLVED IN THE SELECTIVE SOLVENT TO FORM AN EXTRACT, AND PASSING AMIXTURE CONSISTING ESSENTIALLY OF A NON-AROMATIC HYDROCARBONANTI-SOLVENT BOILING BELOW THE AROMATIC HYDROCARBONS IN COMBINATION WITHRECYCLED EXTRACTED AROMATICS COUNTERCURRENTLY THROUGH THE RESULTINGEXTRACT AND RECOVERING THE AROMATIC HYDROCARBONS DISSOLVED IN THEEXTRACT IN PURE FORM.